The present invention generally relates to actuators and more particularly relates to brake calipers relates to an actuating unit.
International patent application WO 99/45292 discloses an electromechanically operating actuating unit of this general type. In the prior-art actuating unit, the force is transmitted from the planet cage to the threaded spindle by means of a positive plug connection that is coupled to the planet cage in a torsion-proof, radially yielding and flexible fashion.
What is disadvantageous in the prior-art actuating unit is that the plug coupling has only one degree of freedom so that all disturbances differing from the degree of freedom of the plug coupling are transmitted. This impairs the efficiency that can be achieved.
In view of the above, an object of the present invention is to disclose an actuating unit of the type initially referred to wherein an increase in efficiency can be achieved.
According to the present invention, this object is achieved in that the force is transmitted from the planet cage to the threaded spindle by means of a coupling shaft, the ends of which form universal joints with the planet cage and the threaded spindle. Preferably, one end of the coupling shaft is accommodated in a hollow spindle member of the threaded spindle.
In another embodiment of the present invention, one end of the coupling shaft is accommodated within the area of the planet cage in an outside ring of a radial bearing that is connected to the planet cage.
In one favorable embodiment used for an electromechanically actuated disc brake for automotive vehicles, the said actuating unit being arranged at a brake caliper in which two friction linings that cooperate with each one lateral surface of a brake disc are arranged so as to be displaceable within limits, wherein one of the friction linings is adapted to be moved into engagement with the brake disc by the actuating unit directly by means of the actuating element and the other friction lining is adapted to be moved into engagement with the brake disc by the effect of a reaction force generated by the brake caliper, wherein the actuating unit comprises an electric motor, the first reducing gear is arranged between the electric motor and the actuating element in terms of effect, and the second reducing gear is arranged between the electric motor and a part of the first reducing gear.
In another embodiment of the subject matter of the present invention, the threaded nut of the ball screw may have a bipartite design, the first part cooperating with the first friction lining, while the conversion of a rotational movement into translation takes place in the second part. It is particularly favorable when the return area for the balls of the ball screw is provided in the second part.
In a design wherein a guide member embracing the threaded nut is provided which is supported on the gearbox case that accommodates the ball screw and on which the threaded spindle is axially supported by means of a radial bead by the intermediary of an axial bearing, it is especially favorable that the rigidity of the radial bead and the area of the guide member opposite the bead are chosen so that the contact surfaces of the axial bearing suffer from an equal deformation during operation. This provision ensures a uniform distribution of the load that acts on the axial bearing, thereby permitting the use of a small bearing that is optimally utilized.
In a favorable aspect of the subject matter of the present invention, wherein the guide member includes force-measuring elements, the said guide member contains an axial groove which accommodates conduits associated with the force-measuring elements. In this arrangement, an electric interface or a plug to which the conduits are connected is preferably arranged in the area of the guide member that faces the friction lining.
In another embodiment of the subject matter of the present invention, the return movement of the balls is through all threads, and the return area for the balls is designed as a rotation prevention mechanism of the threaded nut in the guide member. Expediently, combining two independent functional means in one component optimizes the mounting space.
Besides, it is especially advantageous that the guide member is elastically designed and the threaded nut is arranged in the guide member with a play. It is achieved by this arrangement that the threaded nut is guided only in its rear area by means of the threaded spindle. The disturbances that take effect on the threaded nut are, thus, not supported by way of the sliding friction between the threaded nut and the guide member.